Bitcoin has dropped lately. It has just started to recover. In such periods the ones preaching an even bigger drop (the FUDers) are the more vocal ones.
If Bitcoin will have a sustained growth for a while, the dreamers will kick in, telling about 500k, 1M and maybe even bigger numbers.

So right now your numbers are "a blasphemy"  
Imho yes, 600k is not an unrealistic number. The only problem I see is the timing, that could be wrong. And I think that I know why too: Libra may have no effect at all.